Time base correction (hereinafter referred to as TBC) in which information is written to memory is a type of technology where horizontal sync information generated from a sync signal in a video signal is used to process images from a video signal.
One example of this technology is presented in Japanese patent number 2844765 (xe2x80x9cVideo signal playback devicexe2x80x9d).
FIG. 2 from this patent shows a block diagram of a TBC architecture. The output from a sync separator 33 (indicated in the figure as SYNC SEPA 33) is sent to a timing GEN 35 by way of a PLL 34. A write clock WCK and a write reset pulse WRES, generated by the timing GEN, provide control for write operations to buffer memories 40, 46. There is no description, however, of the sync separator 33 and how the HD signal is generated from the separated composite sync signal.
The basic principle behind the TBC technology described above is as follows. A video input signal containing time base fluctuations is written to memory with a sync signal containing similar time base fluctuations serving as a write trigger. Reading from memory is started using a stable read trigger. For TBC technology involving line memory, the composite sync signal is generally separated from the video input signal and the horizontal sync information HD from which equalizing pulses have been removed is used as the write trigger.
One aspect of improving TBC performance is generating the HD signal so that it faithfully preserves the time base fluctuations of the video input signal. If this is not done effectively, the inconsistencies between the two time base fluctuations will lead to time base fluctuations in the TBC output signal.
Another aspect of improving TBC performance is generating HD interpolation information when there is a dropped sync signal in the video input signal. Without this feature, writes to memory will stop during the corresponding interval, and the image display position of the subsequent TBC output will be shifted upward on the screen.
One method for generating an interpolated HD signal when there is a dropped sync signal involves using PLL technology. A detailed description of PLL technology will be omitted since it is a widely known technology. By using a high PLL time constant setting, an interpolated HD can be generated even if there is some degree of sync dropping. However, if skew is present in the video input signal, the time constant will aggravate the problem. Immediate tracking of the skew in the video signal will be prevented, and the PLL-generated HD signal will indicate the tracking characteristics at the time constant described above. This tracking delay will obstruct generation of an HD that faithfully preserves the time base fluctuations contained in the video input signal, resulting in skewing in the TBC output image.
The object of the present invention is to provide means for generating HD pulses suited for image processing using HD pulses, e.g., TBC memory writing operations. Another object of the present invention is to provide a video signal processing device equipped with the same.
The present invention relates to a video signal processing device including means for processing images writing image information from a video signal to a digital storage medium, means for converting data converting the image information to a predetermined format, or means for display control displaying the image information, and the like. More specifically, the present invention relates to a video signal processing device performing at least part of the processing of image processing means described above using horizontal sync information (hereinafter referred to as HD) generated from a sync signal of the video signal.
The video signal processing device of the present invention includes: means for separating a composite sync signal from a video input signal; means for generating pulses receiving the composite sync signal from sync separating means and generating a horizontal sync information HD; and means for processing images receiving image information contained in the first video signal and the HD information and performing image processing.
Furthermore, pulse generating means includes means for detecting leading edges of the composite sync signal and means for detecting trailing edges. Timing for the HD information is controlled based on the timing of trailing edges.
The present invention provides pulse generating means generating horizontal sync information HD suited for serving as part of image processing means such as means for providing TBC functions, image compression recording/playback functions, and LCD display functions. The present invention also provides a video signal processing device containing the same.